Information recording medium

ABSTRACT

In an information recording medium comprising at least a substrate, a recording layer, and a resin layer, the substrate is formed with at least a pit corresponding to a read only area  31  and a groove corresponding to a recording/reproducing area  32  without overlapping with each other. A reflectivity of the recording layer is specified to be more than 10%. The recording layer and the resin layer are continuously adhered over both the read only and recording/reproducing areas  31  and  32.  The information recording medium is characterized in that both push-pull signal outputs T 1  and T 2,  which are reproduced from the read only area  31  and the recording/reproducing area  32  respectively, are more than 0.1 and satisfy an inequality 1.5≧T 1 /T 2 ≧0.5.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an information recording mediumutilized for an optical recording/reproducing apparatus, which reads outinformation recorded on the information recording medium by making theinformation recording medium relatively move, particularly, relates toan information recording medium comprising a read only area of enablingto read out information and a recording/reproducing area of enabling torecord and reproduce information.

[0003] 2. Description of the Related Art

[0004] Currently various types of information recording mediums such asin a disk shape, in a card shape, and in a tape shape are utilized as anoptical information recording medium from which information is read outby making the information recording medium relatively move. Suchinformation recording mediums are divided into two types inconsideration of mechanism of recording or reproducing: one is a readonly type and the other is a recording/reproducing type, that is, arecordable type and an overwritable type. A read only type informationrecording medium is shipped out into a market with being prerecordedwith information such as a CD audio disk typically, and is reproduced bya user. On the other hand, a recordable or overwritable type informationrecording medium is shipped out into a market without any recordedinformation, and a user records information on it and reproduces it ifnecessary.

[0005] A problem arises along with a trend toward multimedia causing toincrease a chance such that copyright is infringed by using anelectronic means. Accordingly, in order to prevent such the problem, anidea such as embedding a specific code, which can not be rewritten by auser, is necessary to be realized even in a recordable or overwritabletype information recording medium, which can be recorded freely by auser.

[0006] As mentioned above, various kinds of information recordingmediums, which are provided with two areas composed of a read only areaand a recording/reproducing area, have been introduced. For example,there is existed an information recording medium provided with arecording/reproducing area only in a predetermined angle. Further,another information recording medium having a recording/reproducingarea, which is provided with a read only area allocated in each one halftrack, is introduced.

[0007] Furthermore, an information recording medium provided with both aread only area and a recording/reproducing area, which are allocated indifferent positions from each other, is introduced. FIG. 2 is a crosssectional view of such the information recording medium 301. In FIG. 2,the information recording medium 301 comprises a substrate 10, arecording layer 13, and a resin layer 14. A microscopic pattern isformed on a surface of the substrate 10 at a boundary area between thesubstrate 10 and the recording layer 13. Microscopic patternsconstituting a read only area and a recording/reproducing area areengraved in areas corresponding to the read only andrecording/reproducing areas respectively. Actually, microscopic patterns11 corresponding to the read only area and other microscopic patterns 12corresponding to the recording/reproducing area are engraved. Thesemicroscopic patterns 11 and 12 are different from each other in depth. Adepth “d1” of the microscopic patterns 11 is λ/4n, on the other hand, adepth “d2” of the microscopic patterns 12 is λ/8n, wherein λ is areproduction wavelength of a laser beam and “n” is a refractive index ofthe substrate 10 at the reproduction wavelength λ. Specifying the depthof the microscopic patterns 11 to λ/4n is caused by a phase depth inwhich a signal output from the read only area becomes maximum. Further,specifying the depth of the microscopic patterns 12 to λ/8n is caused bythat a push-pull signal related to tracking of the information recordingmedium becomes a maximum output.

[0008] As mentioned above, allocating two areas in different positionsreduces load of a recording/reproducing apparatus due to a simplifiedlayout. Accordingly, there is much merit.

[0009] However, there is existed a following problem of the prior artmentioned above. A defect has occurred when an information recordingmedium formed with microscopic patterns shown in FIG. 2 has been loadedin various recording/reproducing apparatuses, which are currentlyavailable in a market, and operated. A mode of the defect is out oftracking while reproducing the information recording medium withcontinuously traversing from a recording/reproducing area to a read onlyarea. Further, an operation traversing reversely from the read only areato the recording/reproducing area is also defective. According to ourcareful investigation of the problem, it is found that arecording/reproducing apparatus employs a push-pull method for trackingso as to record information in a groove and the push-pull method doesnot match with the information recording medium 301. In other words,firstly, the problem is caused by that forming the read only area in thedepth of d1=λ/4n results a push-pull signal output in zero. In a casethat the push-pull signal output is zero, a track can not be detected.Therefore, the reproduction stops at the track. Further, as a secondproblem, output difference between a push-pull signal output of the readonly area and a push-pull signal output of the recording/reproducingarea is large, so that a servo system of the recording/reproducingapparatus can not follow properly. Accordingly, it is required to solvesuch the problem as out of tracking when an information recording mediumhaving two areas is actually recorded and reproduced.

SUMMARY OF THE INVENTION

[0010] Accordingly, in consideration of the above-mentioned problems ofthe prior art, an object of the present invention is to provide aninformation recording medium, which can solve the problem mentionedabove.

[0011] In order to achieve the above object, the present inventionprovides, according to an aspect thereof, an information recordingmedium, which comprises a substrate, a recording layer, and a resinlayer, wherein the substrate is formed with a pit corresponding to aread only area and a groove corresponding to a recording/reproducingarea without overlapping with each other, and wherein a reflectivity ofthe recording layer is more than 10%, the information recording mediumis characterized in that a push-pull signal output T1 reproduced fromthe read only area and another push-pull signal output T2 reproducedfrom the recording/reproducing area is more than 0.1 respectively andfurther 1.5≧T1/T2≧0.5.

[0012] Other object and further features of the present invention willbe apparent from the following detailed description when read inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

[0013]FIG. 1 is a plan view of an information recording medium in a diskshape according to an embodiment of the present invention.

[0014]FIG. 2 is a cross sectional view of an information recordingmedium common to a prior art and the present invention.

[0015]FIG. 3 is a cross sectional view of an information recordingmedium according to the present invention.

[0016]FIG. 4 is a cross sectional view of an information recordingmedium according to a first embodiment of the present invention.

[0017]FIG. 5 is a plan view of a boundary area between a read only areaand a recording/reproducing area of an information recording mediumaccording to the present invention.

[0018]FIG. 6 is a plan view of a boundary area between a read only areaand a recording/reproducing area of an information recording mediumaccording to the present invention.

[0019]FIG. 7 is a plan view of a boundary area between a read only areaand a recording/reproducing area of an information recording mediumaccording to the present invention.

[0020]FIG. 8 is a plan view of a boundary area between a read only areaand a recording/reproducing area of an information recording mediumaccording to the present invention.

[0021]FIG. 9 is a cross sectional view of a 4-division photodetectorutilized for recording and reproducing an information recording mediumaccording to the present invention.

[0022]FIG. 10 is a graph showing a relation between a depth of a readonly area of an information recording medium and a push-pull signaloutput according to the present invention.

[0023]FIG. 11 is a graph showing a relation between a depth of arecording/reproducing area of an information recording medium and apush-pull signal output according to the present invention.

[0024]FIG. 12 is a plan view of an information recording medium in acard shape according to the present invention.

[0025]FIG. 13 is a plan view of another information recording medium ina card shape according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] With referring to drawings, details common to all embodiments ofthe present invention are explained first.

[0027]FIG. 1 is a plan view of an information recording medium in a diskshape according to an embodiment of the present invention.

[0028]FIG. 2 is a cross sectional view of the information recordingmedium shown in FIG. 1.

[0029]FIG. 3 is another cross sectional view of the informationrecording medium shown in FIG. 1.

[0030] In FIG. 1, an information recording medium 1 in a disk shapecomprises a read only area 31 and a recording/reproducing area 32. Asshown in FIG. 1, the read only area 31 and the recording/reproducingarea 32 is allocated in an innermost circumference area and an outercircumference area of the information recording medium 1 respectively.However, these allocations can be reversely arranged. Further, these twoareas are formed not so as to overlap with each other. Some gap existingbetween two areas can be allowable. Furthermore, a plurality of the readonly and recording/reproducing areas 31 and 32 can also be allowable.

[0031]FIG. 2 shows a fundamental configuration of an informationrecording medium 1 of the present invention. The information recordingmedium 1 of the present invention is resemble to that of the prior artin appearance, so that the same drawing is used for explaining thepresent invention. FIG. 3 also shows a fundamental configuration of aninformation recording medium 2 of the present invention. Theconfiguration shown in FIG. 3 is a same as that shown in FIG. 2 except areading out direction, that is, an optical path. An optical path will beexplained.

[0032] As shown in FIGS. 2 and 3, the information recording medium 1 or2 comprises a substrate 10, a recording layer 13 and a resin layer 14. Amicroscopic pattern is formed on a surface of the substrate 10 at aboundary between the substrate 10 and the recording layer 13.Microscopic patterns 11 and 12 are formed in areas corresponding to theread only area 31 and the recording/reproducing area 32 respectivelywithout overlapping with each other.

[0033] Further, these microscopic patterns 11 and 12 have a depth of“d1” and “d2” respectively. Either cases can be acceptable whether ornot the depth “d1” of the microscopic patterns 11 is a same as-the depth“d2” of the microscopic patterns 12. However, a depth must be designatedso as to be able to obtain a range of push-pull signal output, whichwill be depicted.

[0034] Layers composed of the substrate 10, the recording layer 13, andthe resin layer 14 are formed in parallel to each other. The resin layer14 is adhered on the recording layer 13 with continuously covering overall areas including at least the read only area 31 and therecording/reproducing area 32. Although recording or reproducing bylight beam is performed on the recording layer 13, it is arbitrarilydetermined that a laser beam having a wavelength of λ nm, which isstopped down by a objective lens having a numerical aperture of NA, isirradiated from either side of the information recording medium 1. Inother words, it is arbitrarily determined whether the laser beam isirradiated from the substrate 10 side or the resin layer 14 side.Further, a path of irradiating the laser beam, that is, an optical pathhas a certain refractive index “n” for the wavelength λ. An effectiveoptical length is determined by the refractive index “n”. The substrate10 is illustrated as an optical path in FIG. 2. However, the resin layer14 can be used as an optical path as shown in FIG. 3. The refractiveindex “n” of these optical paths is desirable to be 1.4 through 1.7 inconsideration of interchangeability with current optical disks, moredesirable to be 1.45 through 1.65. Further, if birefringence of theoptical path is designated to be less than 100 nm by double paths,deviation of reproduction output can be sufficiently suppressed, so thatit is most desirable.

[0035] Synthetic resins of high strength and various ceramics can beutilized for a material of the substrate 10. Actual materials are suchresins as polycarbonate, polymethyle methacrylate, polystyrene,polycarbonate-polystyrene copolymer, polyvinyl chloride, alicyclicpolyorefin, polymethyle pentene, polyacetate resin, and variouscopolymer having a resin frame of them, and such synthetic resin asblock polymer, and such ceramics as soda aluminosilicate glass, boronsilicate glass, and silica glass.

[0036] Further, the recording layer 13 is at least made of a recordingmaterial of which a reflectivity is more than 10% at the wavelength λ.Actually, following materials can be used for a recording material ofenabling recordable or write once recording: such dye materials ascyanine dye, phthalocyanine dye, naphthalocyanine dye, azo dye, andnaphthoquinone dye. Furthermore, a phase change recording material, socalled, and a magneto-optical recording material can be used for arecording material of enabling overwrite. Typical phase change recordingmaterials are as follows: alloys made of some materials selected fromindium, antimony, tellurium, selenium, germanium, gallium, bismuth,platinum, gold, silver, copper, tin, sulfur, and aluminum, wherein analloy includes compound such as oxide, nitride, and carbide. Moreover,in a case of magneto-optical recording material, there existed an alloy,which contains at least a transition metal and a rare earth element. Thealloy is made of some materials selected from terbium, cobalt, iron,gadolinium, neodymium, dysprosium, bismuth, palladium, samarium,holmium, praseodymium, manganese, titanium, erbium, ytterbium, lutetium,chromium, tin, platinum, wherein an alloy includes compound such asoxide, nitride, and carbide. In addition thereto, the recording layer 13can be multi-layered or laminated by an optical interference film suchas SiN, SiC, SiO, ZnS, ZnSSiO, AlO, GeN, MgF, InO, and ZrO, and anoptical reflection film such as aluminum, gold, silver, and titanium fora purpose of improving performance. In order to perform high densityrecording and reproducing, the recording layer 13 can be laminated by asuper resolution masking film or a contrast enhancing film, which iscommonly known.

[0037] The resin layer 14 is provided for protecting the recordingslayer 13 chemically and physically, and can be selected fromthermosetting resins, ultra violet ray curable resins, various radiationincluding visible light curable resins, electron beam curable resins,moisture curable resins, and multiple liquid mixture curable resins. Asurface of the resin layer 14 can be printed if necessary.

[0038]FIG. 5 is a plan view of a boundary area between a read only areaand a recording/reproducing area of an information recording mediumpartially enlarged according to the present invention. There existed agap having a distance of “G” (hereinafter referred to a gap “G”) betweenthe read only area 31 and the recording/reproducing area 32 caused by amanufacturing process of the information recording medium 1. In otherwords, as shown in FIG. 5, the gap “G” exists between the microscopicpatterns 11 of the read only area 31 and the microscopic patterns 12 ofthe recording/reproducing area 32. Basically, a recording/reproducingapparatus can jump across the gap “G” by forcing to drive a pickup or alike. According to our experiment, the jumping motion can be smoothlyperformed by setting the gap “G” in less than 25 μm.

[0039] As shown in FIG. 5, the microscopic patterns 11 of the read onlyarea 31 is a group of pit 21, which is engraved by what is called arecording method of cutting. A track is composed of continuing groups ofthe pit 21. The microscopic patterns 12 utilized for therecording/reproducing area 32 are not formed in the read only area 31. Agap between each track is in a distance of P1 (hereinafter referred to atrack pitch P1). The pit 21 is modulated by a well-known modulationmethod and formed a pit in various length. A minimal pit length closelyrelating to quality of a reproduction signal is defined as L1. Thegroups of pit 21 can be meandered or wobbled by applying a sinusoidaldeflection to the pit 21 when the pit 21 is recorded with cutting. It isacceptable that wobbling is recorded by either the CLV (constant linearvelocity) or the CAV (constant angular velocity) method. Further, aspecific code, which can not be rewritten by a user, is recorded in theread only area 31. The specific code is such a key or code as a key forciphering, a key for deciphering, a code for permitting to record, acode for refusing to record, and a disk serial number inherent to eachdisk. In addition thereto, a lead-in signal can be recorded as a samemanner as that of a current read only disk.

[0040] The microscopic patterns 12 in the recording/reproducing area 32are composed of a group of groove 22. A gap between each groove 22 iscalled a land 23 commonly. Each groove 22 is spaced in a distance of P2(hereinafter referred to a track pitch P2). The groove 22 can also bewobbled by applying a sinusoidal deflection to the groove 22 when thegroove 22 is recorded with cutting. It is acceptable that wobbling isrecorded by either the CLV or the CAV method. Further, an address pit,which specifies an address number, can be allocated in between eachgroove 22, that is, in the land 23.

[0041] Recording an information by a user is explained next.

[0042]FIG. 6 is a plan view of the interface area as same as that ofshown in FIG. 5 with showing a mark 24 written in the groove 22.

[0043]FIG. 7 is a plan view of the interface area as same as that ofshown in FIG. 5 with showing the mark 24 written in the land 23.

[0044] Recording is performed as shown in FIG. 6. That is to say, themark 24 is formed in the groove 22 by focusing a laser beam forrecording on the groove 22. The mark 24 is modulated by a well-knownmodulating method, and then formed in various lengths. A minimal pitlength closely relating to quality of a reproduction signal is definedas L2. As shown in FIG. 7, the mark 24 can be written in between eachgroove 22, that is, in the land 23. Further, the mark 24 can be writtenin both the groove 22 and the land 23 although not shown in anydrawings.

[0045] The well-known modulation method applied for the read only andrecording/reproducing areas 31 and 32 is a signal of which minimal marklength is specified to one of lengths such as 2T, 3T, 4T, and 5T. In acase of a signal system in which a minimal pit length or a minimal marklength is specified to 2T, for example, such a signal system as an eightto twelve (8/12) modulation, which is composed of signals from 2T to 8T,can be utilized. Further, in a case of a signal system in which aminimal pit length or a minimal mark length is specified to 3T, signalsystems such as an eight to fourteen (8/14) modulation, an eight tofifteen (8/15) modulation, and an eight to seventeen (8/17) modulation,which are composed of signals from 3T to 11T, and another signal systemsuch as an eight to sixteen (8/16) modulation, which is composed ofsignal from 3T to 11T and 14T, can be utilized. In these read only andrecording/reproducing areas 31 and 32, each signal in the respectiveareas can be modulated by different modification methods. However, asame modification method is desirable to be employed, in considerationof convenience of a recording/reproducing apparatus. It is alsodesirable by the same reason that P1=P2 and L1=L2.

[0046] In order to enable a traverse reproduction over the read onlyarea 31 and the recording/reproducing area 32, the depth d1 and d2 ofrespective areas of the information recording medium 1 according to thepresent invention are adjusted so as to enable to obtain a predeterminedpush-pull signal. A predetermined push-pull signal satisfies followinginequalities simultaneously with defining that a push-pull signal outputof the read only area 31 is T1 and a push-pull signal output of therecording/reproducing area 32 before recording is T2.

[0047] T1≧0.1

[0048] T2≧0.1 and

[0049] 1.5≧T1/T2≧0.5.

[0050] Further, in order to stabilize a traverse reproduction overareas, respective push-pull signal outputs are desirable to be within arange of satisfying following inequalities simultaneously:

[0051] T1≧0.15

[0052] T2≧0.15 and

[0053] 1.4≧T1/T2≧0.6.

[0054] A range of tracking signal of the information recording mediumaccording to the present invention is obtained by a limiting value,which is obtained by reproducing the information recording mediumactually loaded in a player by means of the push-pull method. A resultof experiment is shown in Table 1. By examining tracking ability in theread only area 31 with respect to T1, tracking is completely disabled byT1 in less than 0.08. TABLE 1 T1 Tracking 0.08 Disable 0.10 Enable 0.15Enable 0.18 Enable 0.25 Enable

[0055] Further, Table 2 shows a result of examining tracking ability inthe recording/reproducing area 31 with respect to T2. Tracking iscompletely disabled by T2 in less than 0.08 as same situation as that ofT1. TABLE 1 T2 Tracking 0.08 Disable 0.10 Enable 0.15 Enable 0.22 Enable0.31 Enable 0.45 Enable

[0056] It is found by the above experiment that a value of both T1 andT2 must be more than 0.1. Furthermore, the value is desirable to be morethan 0.15, in consideration of a case that the information recordingmedium 1 is dusted or scratched.

[0057] A limitation of continuous reproducibility over two areas iscaused by that there is existed a limit in a dynamic range of a servocircuit of a recording apparatus. In other words, it is required that adifference between T1 and T2 is smaller. Therefore, with respect to theinformation recording medium 1, which satisfies the inequalities ofT1≧0.1 and T2≧0.1, a limiting value is obtained by performing a traversereproduction over two areas for various disk samples of T1/T2. A resultis shown in Table 3 below. As shown in Table 3, the traversereproduction over two areas is enabled in a case that T1/T2 is within arange from 0.5 to 1.5. However, the value is desirable to be within arange from 0.6 to 1.4, in consideration of a case that the informationrecording medium 1 is dusted or scratched. TABLE 3 T1 T2 T1/T2 Traversereproduction over areas 0.10 0.10 1.0 Enable 0.10 0.20 0.5 Enable 0.100.25 0.4 Disable 0.15 0.22 0.7 Enable 0.20 0.12 1.7 Disable 0.20 0.131.5 Enable 0.20 0.28 0.7 Enable 0.20 0.40 0.5 Enable 0.20 0.45 0.4Disable 0.22 0.16 1.4 Enable 0.25 0.16 1.6 Disable 0.25 0.17 1.5 Enable0.25 0.25 1.0 Enable 0.25 0.34 0.7 Enable 0.25 0.44 0.6 Enable

[0058] A push-pull signal output is defined as follows: a push-pullsignal is a signal, which is produced by calculating respective outputsfrom a 4-division photodetector utilized for a recording/reproducingapparatus as a pickup.

[0059]FIG. 9 is a cross sectional view of a 4-division photodetector 9utilized for recording and reproducing the information recording medium1 according to the present invention.

[0060] In FIG. 9, a horizontal and vertical axes are a radial directionand a tangential direction (track direction) respectively incorresponding to FIGS. 5 through 7. Reproduced outputs of the 4-divisionphotodetector 9 are Ia, Ib, Ic, and Id respectively. An outputdifference between an inner circumference side and an outercircumference side, that is, |(Ia+Ib)−(Ic+Id)| is measured by an AC(alternative current) coupling, and then total outputs, that is,|(Ia+Ib+Ic+Id)| is measured by a DC (direct current) coupling. Apush-pull signal “T” is a ratio of these two values and defined asfollows:

T=|(Ia+Ib)−(Ic+Id)|/|(Ia+Ib+Ic+Id)|.

[0061] As mentioned above, in the information recording medium 1 havingat least the read only and recording/reproducing areas 31 and 32, inorder to enable the traverse reproduction over two areas, the presentinvention specifies a push-pull signal output to a predetermined range.

[0062] [First embodiment]

[0063]FIG. 1 is a plan view of an information recording medium in a diskshape according to an embodiment of the present invention.

[0064]FIG. 4 is a cross sectional view of the information recordingmedium shown in FIG. 1 according to a first embodiment of the presentinvention.

[0065] In FIG. 1, an information recording medium 3 comprises a readonly area 31 formed a ring shape in an inner circumference area and arecording/reproducing area 32 formed a ring shape in an area outside theread only area 31. As shown in FIG. 4, the information recording medium3 comprises a substrate 10, a recording layer 13, a resin layer 14 and adummy substrate 15. The resin layer 14 is adhered on the recording layer13 with continuously covering over two areas including the read onlyarea 31 and the recording/reproducing area 32. The substrate 13comprises polycarbonate of which a refractive index “n” is 1.58 at awavelength λ of 650 nm. The recording layer 13 comprises a phase changematerial having a reflectivity of more than 15% such as an alloy ofantimony, tellurium, and a metal having a melting point of less than1100° C. Actually, the alloy is composed of silver, indium, antimony,and tellurium (AgInSbTe), for example. The alloy is sandwiched bydielectric such as ZnSSiO and further laminated by a reflection film ofan aluminum alloy, and then they are formed as a recording layer havinga reflectivity of 18 to 30%. The resin layer 14 comprises an ultraviolet curable resin and is adhered to the dummy substrate 15 withlaminated.

[0066]FIG. 8 is a plan view of microscopic patterns 11 and 12 formed onthe substrate 10 typically before recording information.

[0067] In FIG. 8, a gap “G” between the microscopic pattern 11 and 12,that is, a gap “G” between the read only area 31 and therecording/reproducing area 32 is 25 μm. The microscopic patterns 11corresponding to the read only area 31 is recorded spirally by the CLVmethod, that is, a group of pit 21, which is wobbled sinusoidally. Awidth of wobbling is 0.009 to 0.017 μm. An average track pitch P1 of themicroscopic patterns 11 is 0.74 μm. With respect to a modificationmethod of the read only area 31, the 8/16-modification method isutilized. A minimal pit length of the pit 21 is 0.4 μm.

[0068] On the other hand, the recording/reproducing area 32 is composedof a sinusoidally wobbled groove 22 and an address pit 25 formed on aland 23, which is provided between each groove 22 with being adjacent toa groove wall. These groove 22 and address pit 25 is also formed in aspiral. A width of wobbling is 0.009 to 0.017 μm. An average track pitchP2 of the microscopic patterns 12 is 0.74 μm. In addition thereto, theaddress pit 25 is a pit recorded with an address, which is useful whenrecording, and is recorded throughout the information recording mediumfrom an innermost circumference area to an outermost circumference areain accordance with a certain rule. Recording is performed by forming amark (not shown) in the groove 22. With respect to a recordingmodulation method of the recording/reproducing area 32, the8/16-modulation method is utilized as same as that of the read only area31. A minimal pit length L2 (not shown) of a recorded mark in the groove2 is 0.4 μm as a same length as the minimal pit length L1.

[0069] When such the information recording medium is reproduced by usinga pickup having a wavelength λ of 650 nm and a numerical aperture NA of0.6, in order to accomplish a range of push-pull signal output, that is,T1≧0.1, T2≧0.1, and 1.5≧T1/T2≧0.5, it is effective to optimize depths d1and d2 of the microscopic patterns 11 and 12 in the read only area 31and the recording/reproducing area 32 respectively.

[0070]FIG. 10 is a graph showing a relation between the depth d1 of theread only area 31 of the information recording medium and a push-pullsignal output T1 according to the present invention. A vertical andhorizontal axes represent a value of (d1×n) divided by λ, that is,(nd1/λ) and a push-pull signal output T1 respectively. The T1 is definedby the sine function of the P1. According to FIG. 10, the (nd1/λ) isspecified to 0.03 through 0.22 so as to realize T1≧0.1. Further, areproduction jitter, which is fluctuation in a time axis direction,decreases as far as the (nd1/λ) approaches to 0.25, so that it is properfor the (nd1/λ) to be 0.12 through 0.22 in a depth.

[0071]FIG. 11 is a graph showing a relation between the depth d2 of therecording/reproducing area 32 of the information recording medium and apush-pull signal output T2 according to the present invention. The T2 isdefined by the sine function of the P2 as same as the T1. However, in acase of a groove, a value of the T2 is: approximately twice a value ofthe T1. According to FIG. 11, the (nd2/λ) is specified to 0.02 through0.23 so as to realize T2≧0.1. Further, when the information recordingmedium is recorded and reproduced, a jitter decreases in conjunctionwith reflectivity, which increase, as far as the (nd2/λ) approaches tozero, so that it is proper for the (nd2/λ) to be 0.02 through 0.12 in adepth.

[0072] Furthermore, a reproduction jitter can be obtained in accordancewith the Annex “F” of JIS-X-6241 (Japanese Industrial Standard).According to the Standard, a jitter is required to be not more than 8%.In other words, if a jitter exceeds 8%, reading out a reproductionsignal is seriously affected by disturbance such as disk tilt. Byrecording and reproducing practically, and by optimizing the depths d1and d2, ranges of (nd1/λ) and (nd2/λ) are as follows:

[0073] (nd1/λ) is within a range from 0.17 to 0.22, wherein the T1 is0.1 through 0.22, and

[0074] (nd2/λ) is within a range from 0.02 to 0.10 wherein the T2 is 0.1through 0.42.

[0075] With referring to FIGS. 10 and 11, (nd1/λ) and (nd2/λ) can beselected out from the ranges shown above so as for the T1/T2 to be 0.5through 1.5. It is specified that (nd1/λ)=0.17 and (nd2λ)=0.06 in thisembodiment. In this case, T132 0.22 and T2=0.31, and then it is obtainedthat T1/T2=0.7. Accordingly, the push-pull conditions of the presentinvention such that T1≧0.1, T2≧0.1, and 1.5≧T1/T2≧0.5 can besufficiently satisfied. Further, reproduction jitter in the read onlyarea 31 and the recording/reproducing area 32 are 7.9% and 6.2%respectively. Both jitter values sufficiently satisfy the standard.Furthermore, by continuously reproducing two areas, it is confirmed thata continuous reproduction can jump across the two areas without anyproblems.

[0076] [Second Embodiment]

[0077] Parameters of this embodiment are a same as those of the firstembodiment except for (nd1/λ)=0.18 and (nd2/λ)=0.08. Further, the gap“G” between the read only area 31 and the recording/reproducing area 32are specified to 20 μm. By these parameters, it is obtained that T1=0.19and T2=0.37, and then T1/T2=0.5 is obtained. Accordingly, the push-pullconditions of the present invention such that T1≧0.1, T2≧0.1, and1.5≧T1/T2≧0.5 can be satisfied. Further, reproduction jitter in the readonly area 31 and the recording/reproducing area 32 are 7.1% and 6.5%respectively. Both jitter values sufficiently satisfy the standard.Furthermore, by continuously reproducing two areas, it is confirmed thata continuous reproduction can jump across the two areas without anyproblems.

[0078] [Third Embodiment]

[0079] Parameters of this embodiment are a same as those of the firstembodiment except for (nd1/λ)=0.175 and (nd2/λ)=0.067. Further, the gap“G” between the read only area 31 and the recording/reproducing area 32are assigned to 0.74 μm, which is the same value as P1 and P2. By theseparameters, it is obtained that T1=0.20 and T2=0.33, and then T1/T2=0.6is obtained. Accordingly, the push-pull conditions of the presentinvention such that T1≧0.1, T2≧0.1, and 1.5≧T1/T2≧0.5 can be satisfied.Further, reproduction jitter in the read only area 31 and therecording/reproducing area 32 are 7.5% and 6.3% respectively. Bothjitter values sufficiently satisfy the standard. Furthermore, bycontinuously reproducing two areas, it is confirmed that a continuousreproduction can be performed without stopping at a boundary between twoareas.

[0080] [Fourth Embodiment]

[0081] Parameters of this embodiment are a same as those of the firstembodiment except for (nd1/λ)=0.2 and (nd2/λ)=0.04. Further, the gap “G”between the read only area 31 and the recording/reproducing area 32 areassigned to 0.74 μm, which is the same value as P1 and P2. By theseparameters, it is obtained that T1=0.15 and T2=0.22, and then T1/T2=0.66is obtained. Accordingly, the push-pull conditions of the presentinvention such that T1≧0.1, T2≧0.1, and 1.5≧T1/T2≧0.5 can be satisfied.Further, reproduction jitter in the read only area 31 and therecording/reproducing area 32 are 6.8% and 5.8% respectively.Both-jitter values sufficiently satisfy the standard. Furthermore, bycontinuously reproducing two areas, it is confirmed that a continuousreproduction can be performed without stopping at a boundary between twoareas.

[0082] [Fifth Embodiment]

[0083] Parameters of this embodiment are a same as those of the firstembodiment except for (nd1/λ)=0.17 and (nd2/λ)=0.04. Further, the gap“G” between the read only area 31 and the recording/reproducing area 32are assigned to 0.74 μm, which is the same value as P1 and P2. By theseparameters, it is obtained that T1=0.22 and T2=0.22, and then T1/T2=1.0is obtained. Accordingly, the push-pull conditions of the presentinvention such that T1≧0.1, T2≧0.1, and 1.5 ≧T1/T2≧0.5 can be satisfied.Further, reproduction jitter in the read only area 31 and therecording/reproducing area 32 are 7.9% and 5.9% respectively. Bothjitter values sufficiently satisfy the standard. Furthermore, bycontinuously reproducing two areas, it is confirmed that a continuousreproduction can be performed without stopping at a boundary between twoareas.

[0084] [Sixth Embodiment]

[0085] Parameters of this embodiment are a same as those of the firstembodiment except for (nd1/λ)=0.17 and (nd2/λ)=0.03. Further, the gap“G” between the read only area 31 and the recording/reproducing area 32are assigned to 0.74 μm, which is the same value as P1 and P2. By theseparameters, it is obtained that T1=0.22 and T2=0.167, and then T1/T2=1.4is obtained. Accordingly, the push-pull conditions of the presentinvention such that T1≧0.1, T2≧0.1, and 1.5 ≧T1/T2≧0.5 can be satisfied.Further, reproduction jitter in the read only area 31 and therecording/reproducing area 32 are 7.9% and 5.5% respectively. Bothjitter values sufficiently satisfy the standard. Furthermore, bycontinuously reproducing two areas, it is confirmed that a continuousreproduction can be performed without stopping at a boundary between twoareas.

[0086] [Seventh Embodiment]

[0087] Parameters of this embodiment are a same as those of the firstembodiment except for (nd1/λ)=0.17 and (nd2/λ)=0.028. Further, the gap“G” between the read only area 31 and the recording/reproducing area 32are assigned to 0.74 μm, which is the same value. as P1 and P2. By theseparameters, it is obtained that T1=0.25 and T2=0.158, and then T1/T2=1.5is obtained. Accordingly, the push-pull conditions of the presentinvention such that T1≧0.1, T2≧0.1, and 1.5≧T1/T2≧0.5 can be satisfied.Further, reproduction jitter in the read only area 31 and therecording/reproducing area 32 are 7.9% and 5.4% respectively. Bothjitter values sufficiently satisfy the standard. Furthermore, bycontinuously reproducing two areas, it is confirmed that a continuousreproduction can be performed without stopping at a boundary between twoareas.

[0088] [Eighth Embodiment]

[0089] An embodiment of the information recording medium, which isrecorded or reproduced by using a blue semiconductor laser beam having awavelength λ of 405 nm is explained next as an expanded embodiment ofthe present invention. An information recording medium 2 has a crosssectional configuration shown in FIG. 3. The information recordingmedium 2 comprises a substrate 10 composed of polycarbonate, a recordinglayer 13 composed of a phase change material having reflectivity of morethan 10%, particularly, an alloy composed of antimony, tellurium, and ametal having a melting point of less than 1100° C., and a resin layer14. Further, the recording layer 13 actually comprises an alloy composedof silver, indium, antimony, and tellurium (AgInSbTe), for example. Thealloy is sandwiched by dielectric such as ZnSSiO and further laminatedby a reflection film of an aluminum alloy, and then they are formed as arecording layer having a reflectivity of 10 to 25%. The resin layer 14comprises polycarbonate having a refractive index “n” of 1.6 at thewavelength λ of 405 nm.

[0090] Microscopic patterns on a surface of the substrate 10 in both theread only area 31 and the recording/reproducing area 32 are recordedspirally by the CAV method with being wobbled sinusoidally. Otherparameters are the same as those of the first embodiment except for anaverage track pitch such that P1 and P2 is 0.374 μm, wherein respectivewidth of wobbling is 0.006 to 0.011 μm. With respect to a modificationmethod, the D8/15-modification method, which is one variation of the8/15-modulation method and disclosed in the Japanese Patent ApplicationNo 11-23316/1999, is utilized. A minimal pit length L1 and a minimalmark length L2 is 0.2 μm respectively.

[0091] Parameters in the read only and recording/reproducing areas 31and 32 are specified to (nd1/λ)=0.18 and (nd2/λ)=0.08 respectively.Further, the gap “G” between the read only area 31 and therecording/reproducing area 32 are specified to 0.374 μm, which is thesame value as P1 and P2. By these parameters, it is obtained thatT1=0.19 and T2=0.38, and then T1/T2=0.5 is obtained. Accordingly, thepush-pull conditions of the present invention such that T1≧0.1, T2≧0.1,and 1.5 ≧T1/T2≧0.5 can be satisfied. Further, by continuouslyreproducing two areas, it is confirmed that a continuous reproductioncan jump across the two areas without any problems.

[0092] [Ninth Embodiment]

[0093] Parameters of this embodiment are a same as those of the seventhembodiment except for (nd1/λ)=0.17 and (nd2/λ)=0.028. Further, the gap“G” between the read only area 31 and the recording/reproducing area 32are assigned to 0.374 μm, which is the same value as P1 and P2. By theseparameters, it is obtained that T1=0.26 and T2=0.17, and then T1/T2=1.5is obtained. Accordingly, the push-pull conditions of the presentinvention such that T1≧0.1, T2≧0.1, and 1.5 ≧T1/T2≧0.5 can be satisfied.Further, by continuously reproducing two areas, it is confirmed that acontinuous reproduction can be performed without stopping at a boundarybetween two areas.

[0094] While the invention has been described above with reference tospecific embodiments thereof, it is apparent that many changes,modifications and variations in the arrangement of equipment and devicesand in materials can be made without departing from the inventionconcept disclosed herein.

[0095]FIG. 12 is a plan view of an information recording medium in acard shape according to the present invention.

[0096]FIG. 13 is a plan view of another information recording medium ina card shape according to the present invention.

[0097] Each composing element in some embodiments shown by drawings canbe interchanged or replaced by other composing element described in thespecification. For example, in the first and second embodiments, theinformation recording medium is exemplified by a disk shaped one.However, as shown in FIG. 12, an information recording medium 101 in acard shape provided with a read only area 131 in a stripe and arecording/reproducing area 132 in a stripe can be utilized. Further, asshown in FIG. 13, an information recording medium 201 in a cardashapeprovided with a read only area 231 in a ring shape and arecording/reproducing area 232 in a ring shape can also be utilized.

[0098] Furthermore, in the first and second embodiments, a phase changerecording material is utilized for the recording layer 13. However, thematerial is not limited to a phase change recording material. Amagneto-optical recording material and a recordable type recordingmaterial such as a dye material can also be utilized.

[0099] More, a wavelength of a laser beam utilized for reproducing orrecording/reproducing is specified as 650 and 405 nm. However, awavelength is not limited to them. Any length such as 830, 635, 515,460, 430, and 370 nm, and their adjacent wavelength can be utilized.Moreover, with respect to a numerical aperture NA of a lens, any NA suchas 0.4, 0.45, 0.55, 0.65, 0.7, 0.75, 0.8, 0.85, and 0.9 other than 0.60can be applicable. In addition thereto, a lens having an NA of more than1.0, which is represented by a solid immersion lens, can also beapplicable.

[0100] According to an aspect of the present invention, as depictedabove, the information recording medium, which comprises at least theread only area 31 and the recording/reproducing area 32, can perform atraverse reproduction over two areas by specifying push-pull signaloutputs from the read only area 31 and the recording/reproducing area 32to a predetermined range.

What is claimed is:
 1. An information recording medium comprising asubstrate, a recording layer, and a resin layer, wherein said substrateis formed with a pit corresponding to a read only area and a groovecorresponding to a recording/reproducing area without overlapping witheach other, and wherein a reflectivity of said recording layer is morethan 10%, said information recording medium is characterized in that apush-pull signal output T1 reproduced from said read only area andanother push-pull signal output T2 reproduced from saidrecording/reproducing area is more than 0.1 respectively and further1.5≧T1/T2≧0.5.
 2. The information recording medium in accordance withclaim 1, wherein said recording layer comprises a phase change materialso as for a reflectivity of said recording layer to be more than 15%. 3.The information recording medium in accordance with claim i, whereinsaid information recording medium is characterized in that (nd1/λ) and(nd2/λ) is specified to be 0.12 to 0.22 and 0.02 to 0.12 respectivelywith defining a refractive index of said substrate at a reproductionwavelength λ to “n”, a depth of said read only area to d1, and a depthof said recording/reproducing area to d2.
 4. The information recordingmedium in accordance with claim 1, wherein a track pitch Pi of said readonly area and another track pitch P2 of said recording/reproducing areais equal to each other, and a minimal pit length L1 in said read onlyarea and a minimal mark length L2 in said recording/reproducing area isequal to each other.
 5. The information recording medium in accordancewith claim 1, wherein a gap between said read only area and saidrecording/reproducing area is specified to be less than 25 μm.